Disclosure
During the past 30 years, medicine has undergone a transformation in regard to both technology and insight to diseases that have puzzled clinicians over the centuries. As physiology, genetics, bioengineering, and medical practice and ethics have evolved, anatomy is the one constant factor in this field. Anatomy not only serves as the foundation to medicine but also is the cornerstone for surgeons.
The arterial supply to the orbit derived its origin from the internal carotid artery (ICA). In the head and the neck, the common carotid bifurcates at the C4-C5 region. This bifurcation leads to the external carotid artery and the ICA. The external carotid artery is an important vessel because of its blood supply to the orbit, dura, and cranial nerves. The important branches involved in irrigating the orbit include the following:
Internal carotid artery In addition to supplying the anterior part of the brain, eye, and adnexa, the ICA sends branches to both the forehead and the nose. The course and relations of this vessel may be divided into 4 portions: cervical, petrous, cavernous, and cerebral. The length of the ICA varies according to the length of the neck and the point of bifurcation of the common carotid. Although rare, it sometimes arises from the arch of the aorta. Instead of being straight, the course of the ICA is often very tortuous. Branches from the ICA are numerous, and they are not within the scope of this article. This article primarily discusses the branches and the tributaries that irrigate the orbit. Interestingly, the cervical portion of the ICA gives off no branches. The ICA provides both collateralization with the middle meningeal artery and lacrimal and ethmoidal anastomoses. Ophthalmic artery The ophthalmic artery (arteria ophthalmica) is the major blood supply of the orbit. It arises from the ICA (first branch of the ICA), as the ICA is emerging from the cavernous sinus, on the medial side of the anterior clinoid process. It enters the orbital cavity through the optic foramen, below and lateral to the optic nerve. The ophthalmic artery passes over the nerve (in 85% of cases) to reach the medial wall of the orbit. Then, the artery proceeds forward horizontally, beneath the lower border of the superior oblique muscle, and divides into 2 terminal branches, frontal and dorsal nasal. As the artery crosses the optic nerve, it is accompanied by the nasociliary nerve and is separated from the frontal nerve by the superior rectus muscle and the superior levator palpebral muscle. The ophthalmic artery rarely arises from the middle meningeal artery. Most branches of the ophthalmic artery arise in the posterior one third of the orbit and pass anteriorly. As outlined below, the branches of the ophthalmic artery are divided into an orbital group, distributing vessels to the orbit and surrounding parts, and an ocular group, distributing vessels to the muscles and bulb of the eye.
Lacrimal artery One of the largest branches derived from the ophthalmic artery, the lacrimal artery (arteria lacrimalis) arises close to the optic foramen and, not infrequently, is given off before the ophthalmic artery enters the orbit. Interestingly, the lacrimal artery has a variable origin. This artery runs along the lateral wall of the orbit, accompanying the lacrimal nerve along the upper border of the lateral rectus muscle, and supplies the lacrimal gland. Branches of the lacrimal artery include the following:
Supraorbital artery The supraorbital artery (arteria supraorbitalis) arises from the ophthalmic artery, superiorly, as that vessel crosses over the optic nerve. The supraorbital artery passes upward on the medial borders of the superior rectus muscle and the levator palpebral muscle. The supraorbital nerve accompanies the supraorbital artery between the periosteum and the levator palpebral muscle to the supraorbital foramen. As the supraorbital artery passes through the supraorbital foramen, it divides into a superficial branch and a deep branch, which supply the eyebrow and the forehead. It anastomoses with the frontal artery, the frontal branch of the superficial temporal artery, and the supraorbital artery of the opposite side. Within the orbit, the supraorbital artery supplies the superior rectus muscle and the levator palpebral muscle. Furthermore, it sends a branch across the pulley of the superior oblique muscle to supply the medial palpebral commissure. Ethmoidal artery The ethmoidal artery branches into the posterior and anterior ethmoidal arteries. The posterior ethmoidal artery, the smaller of the 2 branches, arises from the ophthalmic artery as it passes along the medial wall between the superior oblique muscle and the medial rectus muscle. This vessel passes through the posterior ethmoidal canal, supplying the posterior ethmoidal cells. In the orbit, this vessel can irrigate the superior oblique muscle, the superior and medial recti muscles, and the superior levator palpebral muscle. The anterior ethmoidal artery accompanies the nasociliary nerve and exits the orbit through the anterior ethmoidal foramen. In the orbit, it supplies the superior oblique muscle. This vessel also supplies the anterior and middle ethmoidal cells, frontal sinus, lateral wall nose, and nasal septum. Medial palpebral arteries The superior and inferior medial palpebral arteries (arteriae palpebrales mediales, internal palpebral arteries) arise from the ophthalmic artery, opposite the pulley of the superior oblique muscle. These vessels leave the orbit to encircle the eyelids near their free margins, forming a superior arch and an inferior arch between the orbicularis oculi and the tarsi. The superior medial palpebral artery anastomoses with the zygomatico-orbital branch of the temporal artery at the lateral angle of the orbit. This artery also anastomoses with the upper of the 2 lateral palpebral branches from the lacrimal artery. The inferior medial palpebral artery anastomoses with the lower of the 2 lateral palpebral branches from the lacrimal artery at the lateral angle of the orbit; with the transverse facial artery; and, at the medial part of the eyelid, with a branch from the angular artery. From this last anastomosis, a branch passes to the nasolacrimal duct, ramifying in its mucous membrane, as far as the inferior meatus of the nasal cavity. Both the superior and inferior medial palpebral arteries supply the lacrimal sac. Frontal artery One of the terminal branches of the ophthalmic artery, the frontal artery (arteria frontalis) leaves the orbit at its medial angle above the trochlea with the supratrochlear nerve, ascending on the forehead, and supplies the forehead and the scalp. The frontal artery anastomoses with both the supraorbital artery and the contralateral vessels. Dorsal nasal artery The dorsal nasal artery (arteria dorsalis nasi, nasal artery), the other terminal branch of the ophthalmic artery, leaves the orbit above the medial palpebral tendon. After giving off a branch to the upper part of the lacrimal sac, it divides into 2 branches, one of which crosses the root of the nose. The dorsal nasal artery anastomoses with the angular artery, a terminal branch of the facial artery. Central retinal artery The central retinal artery (arteria centralis retinae) is the first and one of the smallest branches of the ophthalmic artery. It arises in the posterior one third of the ophthalmic artery. The central retinal artery travels for a short distance beneath the optic nerve, entering the dural sheath of the optic nerve about 5-15 mm behind the globe. It pierces the optic nerve obliquely and travels forward through the central optic nerve. This artery is the principal blood vessel that irrigates the retina. Ciliary arteries The ciliary arteries (arteriae ciliares) are divided into 3 groups: short posterior, long posterior, and anterior ciliary arteries. The short posterior ciliary arteries may number 6-12 vessels. Arising from the ophthalmic artery or its branches, the short posterior ciliary arteries travel anteriorly around the optic nerve to the posterior part of the eyeball, piercing the sclera around the entrance of the nerve. It supplies the choroid and ciliary processes. The 2 long posterior ciliary arteries pierce the sclera posteriorly, a short distance from the optic nerve. They travel forward between the sclera and the choroid, to the ciliary muscle, where they divide into 2 branches. These branches form an arterial circle, the circulus arteriosus major, around the circumference of the iris. Numerous converging branches from the circulus arteriosus major run in the substance of the iris to its pupillary margin, where they form a second arterial circle, the circulus arteriosus minor. The long and short posterior ciliary arteries give collateralization to all the recti muscles, except the lateral rectus muscle. The anterior ciliary arteries are derived from the muscular branches. They travel to the front of the eye to form a vascular zone beneath the conjunctiva. Then, they pierce the sclera, a short distance from the cornea, and end in the circulus arteriosus major. Muscular branches The muscular branches (rami musculares) arise from a common trunk, leading to the superior (lateral) branch and the inferior (medial) branch. The muscular branches enter the sclera anterior to tendon insertions of the recti muscles and anastomose with the long posterior ciliary arteries. The superior (lateral) branch supplies the levator muscle, the superior rectus muscle, the superior oblique muscle, and a portion of the lateral rectus muscle. The lacrimal artery irrigates the remaining portion. The inferior (medial) branch supplies the medial rectus muscle; the inferior rectus muscle; the inferior oblique muscle; and, sometimes, the lateral rectus muscle. This vessel gives off most of the anterior ciliary arteries. Additional muscular branches are given off from the lacrimal and supraorbital arteries or from the trunk of the ophthalmic artery. All the recti muscles have 2 anterior ciliaries, except the lateral rectus muscle. |
|
||||||||||||||||||||||||||||||||||||||||||||
The venous drainage system is comprised of the following:
The blood supply to the eyelid includes the following:
| |||||||||||||||||||||||||||||||||||||||||||||
){kind=small}
